The present invention relates generally to sensors, and specifically to a capacitive type physical quantity detecting sensor for detecting physical quantities along plural axes.
JP-A-2000-81449 (USP 6,257,061) discloses a capacitive type physical quantity detecting sensor with a malfunction self diagnosis function. The capacitive type physical quantity detecting sensor diagnoses malfunctions itself by using the resonance of the sensor elements generated based on the frequency (hereinafter referred to as self diagnosis frequency) of an applied electrical voltage.
However, if the above mentioned technology is applied to a capacitive type physical quantity detecting sensor for detecting physical quantities along two directional axes, since the self diagnosis frequency is used to create resonance of the sensor elements, another resonance is simultaneously generated between both sensor elements. That is, the sensor elements interfere with each other during self diagnosis so that a resonance, which is different from the resonance being used for the diagnosis, is generated. Accordingly, an accurate sensor output that is expected during self diagnosis cannot be obtained.
It is therefore an object of the present invention to provide a capacitive type physical quantity detecting sensor that is capable of obviating the above problems.
It is another object of the present invention to provide a capacitive type physical quantity detecting sensor that is capable of diagnosing malfunctions along plural axes.
In the capacitive type physical quantity detecting sensor of the present invention, during a normal physical quantity detection timing interval, a control signal generator transmits a first signal to a movable electrode and a fixed electrode to detect a change in capacitance between the movable electrode and the fixed electrode. During a self diagnosis timing interval, the control signal generator also transmits a second signal to the movable electrode and the fixed electrode to move the movable electrode for diagnosing a malfunction of each physical quantity detection portion. The control signal generator transmits the second signal to the movable electrode and the fixed electrode of each physical quantity detection portion during different timing intervals.
According to the capacitive type physical quantity detecting sensor of the present invention, the resonance of sensor elements of one of the plurality of physical quantity detection portions does not affect that of the sensor elements of the others of the plurality of physical quantity detection portions. Therefore, sensor output error decreases. As a result, it is possible to diagnose sensor malfunction accurately along each axis of the multi-axis capacitive type physical quantity detecting sensor.
In a capacitive type physical quantity detecting sensor of the present invention, a first frequency of a second signal transmitted to a first one of the plurality of quantity detection portions is different from a second frequency of the second signal transmitted to a second one of the plurality of the physical quantity detection portions.
As a result, it is possible to diagnose sensor malfunction accurately along each axis of the multi-axis capacitive type physical quantity detecting sensor.